System and methods for improved access to vertebral bodies for kyphoplasty, vertebroplasty, vertebral body biopsy or screw placement

ABSTRACT

A method of determining the size and placement of screws in pedicles in a selected spinal area comprising, hollowing out the vertebra in a three-dimensional image of the spine with cortical wall thicknesses selected by a surgeon; determining the isthmus within each pedicle; generating a straight line starting at the center of the isthmus and extending inwardly to a point centered within the anterior cortex so that it is positioned concentrically within the pedicle without touching the walls thereof, the line terminating a predetermined distance from the anterior inner cortical wall and extending outwardly in the opposite direction to penetrate the posterior pedicle cortex; expanding the line concentrically and radially to a cross sectional size that is less than that of the isthmus, the line being expanded into a cylinder that stops growing when any portion thereof contacts the inner cortical wall of the hollowed out vertebral body.

This application claims the benefit of U.S. Provisional PatentApplication No. 60/658,576 filed on Mar. 7, 2005.

FIELD OF THE INVENTION

The present invention relates to the general field of spinal surgeryand, more particularly, to a manual, computerized or automated methodfor the accurate sizing and placement of instruments or screws inpedicles during spinal surgical procedures.

BACKGROUND OF THE INVENTION

Many medical conditions impact on the human spine anatomy. With thegrowing elderly population there are an increasing number of patientswho are sustaining osteopenic or osteoporotic vertebral body compressionfractures that creates significant morbidity and/or mortality for them.Traditional methods for dealing with these compression fractures are notalways very effective. As a result, methods to strengthen the vertebralbody have evolved with significant clinical improvement for affectedpatients. A common procedure for this is vertebroplasty in which a bonesubstitute, such as polymethylmethacrylate, hydroxylapatite compound orother material is injected into the vertebral body usually through atranspedicular approach, through the vertebral body pedicle, andsometimes through an extrapedicular approach. An improvement upon thevertebroplasty is the kyphoplasty procedure in which a balloon catheteris introduced usually through a transpedicular approach into thevertebral body and the catheter is then inflated to nearly restore theoriginal vertebral body anatomy. When the catheter is deflated it leavesbehind a cavitary void which is then filled with materials similar tothe vertebroplasty. Both of these procedures have significant benefitfor the patient in that they are usually performed through apercutaneous method which allows for outpatient management.Occasionally, treated patients may need to have an overnight hospitaladmission.

The use of vertebroplasty and kyphoplasty has extended to includemanagement of vertebral body tumors, traumatic burst fractures andsometimes prophylactic management of impending fractures. A key elementof eligible criteria for either procedure has traditionally been thatthe vertebral body must have an intact posterior vertebral body wall toavoid iatrogenic injury to the spinal cord secondary to leakage ofinjected material.

To reduce iatrogenic injury a number of safeguards have been instituted.Some of these safeguards include use of a radioopaque contrast materialmixed with the injected material to visualize under radiographic imaging(fluoroscopy); performing the procedure in a controlled environment withbiplanar fluoroscopic imaging (anterior-posterior and lateral imaging);miniaturization of equipment to prevent pedicle cortical wall breach,bilateral transpedicular approaches to vertebral bodies to maximizevolume of injected material; limiting number of vertebral bodiesinjected at one setting to three or less vertebral bodies; limitingkyphoplasty to vertebral bodies below thoracic level 4 T4; and otherstrategies.

Inherent to successful outcome of procedures such as vertebroplasty,kyphoplasty, vertebral body biopsy, pedicle screw placement or others isa consistently same and reproducible access to the vertebral body. Thisaccess is usually a transpedicular approach, but can also be performedthrough an extrapedicular approach.

This invention provides a safe and reproducible method to transpedicularand extrapedicular approaches to any vertebral body. Furthermore, itincludes specific embodiments to improve current methods ofvertebroplasty, kyphoplasty, vertebral body biopsy and pedicle screwplacement. This invention reduces radiographic imaging for theseprocedures to primarily anterior-posterior fluoroscopic visualizationand can be utilized in either a percutaneous or open surgicalenvironment with pedicle screw instrumentation present or absent.

The critical parameters for performing any of these procedures arethrough knowledge of the pedicle diameter, length and trajectory andthen actual placement of instruments and/or screws. To date many of theimage guided systems allow for manual determination of these parametersand to improve a surgeon's manual performance in these procedures. As ofyet, no invention or system is available which will automaticallydetermine ideal pedicle diameter, length, trajectory and actualplacement of instruments or screws.

SUMMARY OF THE INVENTION

This invention will automatically generate a table providing the maximumallowable pedicle diameter and length, summary data on trajectory andalso generate a schematic diagram illustrating this data for individualvertebral pedicles. The numeral data can be utilized by the surgeon foractual intraosseous transpedicular access by one of five methods:(Method A) manual instrument or screw placement by the surgeon'spreferred method. (Method B) utilize pedicle base circumference outlinemethod using a variable length adjustable awl combined withintraoperative fluoroscopy, or (Method C) automated instrument or screwplacement using the two ring aligning apparatus and drill guide methodor (Method D) with any commercially available computedtomography/fluoroscopy registration software. This invention also allowsfor extraosseous or extrapedicular pedicle instrument or screw placement(Method E) if a surgeon should so desire based on a trajectory beginningat the same starting point of the anterior cortex but angledtangentially to any distance or angle to surgeon's desired preference.Furthermore, this invention allows trajectory of instrument or screwplacement to proceed along a planned eccentric placement that istranspedicular but centered within the pedicle isthmus (Method F).

One method of the present invention generally comprises the followingsteps:

1. A computed tomography scan (CT), magnetic resonance image (MRI), CTcapable fluoroscopy or similar two dimensional imaging study of thespine area of interest may first be obtained.

2. A dimensionally true three dimensional computer image of the bonyspine is generated from the CT, MRI or other studies, or in any othersuitable manner.

3. The computer generated three dimensional individual vertebra are thenhollowed out by a computer or other device similar to an eggshelltranspedicular vertebral corpectomy to the specifications desired by thesurgeon, e.g., thickness of cortical wall remaining in the vertebralbody cortices or pedicle walls. The individual vertebra can bevisualized as a structure which has been cored or hollowed out and theresulting remaining vertebral body is highlighted throughout its walls.

4. A computer then automatically determines the maximum allowableinstrument or screw diameter to be placed by determining the narrowestdiameter or smallest cross sectional area (isthmus) within any givenpedicle based on surgeon pedicle cortical wall diameter preferences.

5. A computer, for normal vertebra, then generates an elongated cylinderby starting at the center of the isthmus as a straight line whichdetermines the ideal trajectory and extends in opposite directions e.g.,perpendicular to the plane of the isthmus so that it is positionedconcentrically as much as possible within the pedicle without touchingthe remaining highlighted cortex. This line is allowed to penetrate thedorsal or posterior pedicle cortex so that it can extend beyond the skinof a patient to any desired length. The line terminates inside thevertebral body to within a surgeon's predetermined distance from thepredefined anterior inner cortical wall so that it cannot penetrate it.

6. A computer, for fractured vertebra, then generates an elongatedcylinder by starting at the center of the isthmus as a straight linewhich projects to the point centered within the anterior vertebral bodyto determine this ideal trajectory and extends posteriorly withouttouching the remaining highlighted cortex. This line is allowed topenetrate the dorsal or posterior pedicle cortex so that it can extendbeyond the skin of a patient to any desired length. The line terminatesinside the vertebral body to within a surgeon's predetermined distancefrom the predefined anterior inner cortical wall so that it cannotpenetrate it.

7. A computer then builds the line concentrically in radial directionsto a final maximum diameter which will not exceed the narrowest definedpedicle diameter based on surgeon preference pedicle conical wallthickness. This concentric building grows into a visible cylinder whichstops building when any point on its outer surface comes into “contact”with the highlighted inner cortical wall. This rule, however, does notapply to the posterior cortex adjacent to the existing straighttrajectory line generated from the isthmus.

8. A computer then determines the length of the screw by measuring thelength of the cylinder starting at the pedicle base circumference up toits intersection with the dorsal/posterior cortex.

9. A computer then determines the length of the screw by measuring thelength of the cylinder starting at the predefined anterior inner cortexup to its intersection with the dorsal/posterior cortex. To facilitatethe placement of instruments or screws in accordance with one of theautomated methods described hereinafter, the cylinder may be extendedbeyond its intersection with the dorsal/posterior cortex.

10. A computer then provides a data summary table which displays theideal pedicle instrument or screw diameter, length or trajectory foreach individual vertebra pedicle and an idealized schematic drawing ofsame.

11. The tabulated can be utilized to determine the viability of usingpedicle instruments or screws based on maximal pedicle instrument orscrew diameter and length, and also for placement of instruments orscrews by a surgeon's preferred method, such as one of the methodsdescribed hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are three dimensional computer images of the side andback, respectively, of the bony spine made from CT, MRI or other studiesof the spine area of interest;

FIG. 2 illustrates three dimensional computer images of individualvertebra undergoing a manual eggshell corpectomy from the spine areashown in FIGS. 1 a and 1 b;

FIG. 3 is a computer image of a hollowed out individual vertebra showingthe narrowest diameter or cross sectional area (isthmus) within thepedicle;

FIG. 4 is a computer image view of a hollowed out individual vertebrashowing the generation of the straight line through the center of theisthmus and extending in opposite directions through the posteriorpedicle cortex and toward the anterior inner cortex;

FIG. 5 is a schematic drawing showing the generation of the cylinder bybuilding the line extending through the center of the isthmusconcentrically in radial directions;

FIGS. 6 a and 6 b are schematic images of hollowed out individualvertebra that are of symmetrical and irregular shape, respectively;

FIGS. 7 a and 7 b are schematic views showing the isthmus of straightand curved pedicles, respectively;

FIG. 8 is a schematic view of a hollowed out vertebra showing the lengthof the cylinder for determining pedicle screw length;

FIG. 9 is a schematic side elevational view of the individual vertebralabeled by a surgeon for pedicle screw installation;

FIG. 10 a is a data summary table generated by a computer of maximumpedicle screw diameter and length, and also of the trajectory angle ofthe pedicle screw with respect to the sagittal and transverse planes;

FIG. 10 b is a schematic side view of a vertebra showing the sagittalplane and the nature of the trajectory angles in FIG. 10 a; and

FIG. 10 c is a schematic plan view of a vertebra showing the transverseplane and the nature of the trajectory angles in FIG. 10 a;

FIG. 10 d is a schematic rear view of a vertebra showing the coronalplane and the nature of the trajectory angles in FIG. 10 a;

FIG. 11 is a computer generated schematic view of the ideal pediclescrew placements as identified in the data summary table of FIG. 10 a inAP plane demonstrating coronal trajectory;

FIG. 12 is a table of maximum available screw size parameterscorresponding to the data in the summary table of FIG. 10 a and pediclebase circumference outlines (coronal planes) and pedicle distance pointsA-B;

FIG. 13 is a computer generated schematic view of the screw placementsas identified in the table of FIG. 12;

FIG. 14 a is a schematic side elevational view of a vertebra showing theisthmus and the pedicle base circumference;

FIG. 14 b is a schematic plan view of a vertebra showing the computergenerated pedicle cylinder extending through the pedicle basecircumference in the transverse and coronal planes;

FIGS. 14 c, 14 d and 14 e are plan views of vertebra in the lumbar,thoracic and cervical regions, respectively, showing the relationshipbetween the isthmus and the pedicle base circumference in each vertebra;

FIGS. 14 f and 14 g are schematic rear elevational views of a vertebrashowing the positioning of an awl for creating the pedicle screw pilothole in the vertebra;

FIG. 14 h shows schematic and aligned plan and rear elevational views ofa vertebra with a manually determined pedicle screw directional lineextending through the center of the pedicle base circumference;

FIGS. 15 a, 15 c and 15 e show schematic rear elevational views of avertebra in different orientations with a computer generated pediclescrew cylinder extending through the pedicle base circumference thereof;

FIGS. 15 b, 15 d and 15 f show schematic side elevational views of thevertebra illustrated in FIGS. 15 a, 15 c and 15 e, respectively;

FIG. 16 shows CT transaxial views through the center of pedicles T1, T2,T4 and T5 demonstrating pedicle morphology, isthmus and determination ofpedicle pilot hole entry points correlating with intraoperative APfluoroscopic images of each respective vertebra;

FIGS. 17 a and 17 b are side elevational views of different embodimentsof an adjustable awl of the present invention;

FIG. 18 a is a schematic view of an intraoperative AP fluoroscopic imageof individual vertebral and pedicle base circumferences;

FIG. 18 b is a schematic view of computer generated three dimensionalimages of vertebra with computer placed pedicle cylinders and pediclebase circumferences;

FIG. 18 c is a schematic view of the registered images of FIGS. 18 a and18 b;

FIG. 19 a is a schematic side elevational view of a dual ring pediclescrew aligning apparatus constructed in accordance with the presentinvention;

FIG. 19 b is a front elevational view of the apparatus shown in FIG. 19a;

FIGS. 19 c and 19 d are schematic plan views of a vertebra showing theuse of the dual ring pedicle screw aligning apparatus in a percutaneousenvironment and an open surgical environment, respectively;

FIG. 20 is a front elevational view of a modified dual ring pediclescrew aligning apparatus;

FIGS. 21 a and 21 b are side and front elevational views of the endportion of a first embodiment of a drilling cannula member for the dualring aligning apparatus shown in FIGS. 19 a and 19 b;

FIGS. 22 a and 22 b are side and front elevational views of the endportion of a second embodiment of a drilling cannula member for the dualring aligning apparatus shown in FIGS. 19 a and 19 b;

FIG. 23 a is a perspective view of a slotted outer cannula for use withthe dual ring aligning apparatus of FIGS. 19 a and 19 b;

FIG. 23 b is a front elevational view of the slotted cannula shown inFIG. 23 a with an aligning ring disposed therein;

FIG. 24 is a schematic view of a hollowed out vertebra showing differentpedicle screw trajectories in a centered or ideal trajectory and anextraosseous or extrapedicular trajectory that is offset tangentiallyfrom the centered trajectory;

FIG. 25 is a schematic plan view of a vertebra showing the installationof a pedicle screw in accordance with the method of the presentinvention;

FIGS. 26 a, 26 b and 26 c are schematic side elevational, plan and rearelevational views, respectively, of a vertebra showing thecomputer-generated pedicle cylinder extending through the pedicle basecircumference and isthmus;

FIGS. 27 a,27 b and 27 c are schematic views similar to FIGS. 26 a, 26 band 26 c, respectively, showing the computer generated pedicle cylinderfor eccentric placement in vertebras which have fractures and associatedabnormal anatomy;

FIGS. 28 a, 28 b and 28 c are schematic views similar to FIGS. 27 a,27 band 27 c, respectively, showing the computer generated pedicle cylinderfor a modified eccentric placement in vertebras;

FIG. 29 is a schematic rear elevational view of a vertebra and anawl/guide wire to be inserted therein in accordance with the method ofthe present invention;

FIG. 30 is a schematic view similar to FIG. 29 wherein the awl/guidewire is partially inserted in the vertebra;

FIG. 31 is a schematic view similar to FIGS. 29 and 30, respectively,wherein the awl/guide wire is fully inserted in the vertebra;

FIG. 32 is a schematic view similar to FIG. 31, wherein a drill bit isinserted in the vertebra over the guide wire;

FIG. 33 is a schematic view similar to FIG. 31, wherein a first annulais inserted in the vertebra over the guide wire;

FIG. 34 is a schematic view similar to FIG. 33, showing the firstcannula inserted in the vertebra and a second cannula to be inserted inthe first cannula;

FIG. 35 is a schematic view similar to FIG. 34, wherein the secondcannula is inserted in the first cannula;

FIG. 36 is a schematic view similar to FIG. 35, showing a catheter orsimilar device is inserted in the vertebra through the second and/orfirst cannulas;

FIG. 37 is a schematic view similar to FIG. 36 wherein a ballooncatheter is inserted in the vertebra through the second and/or firstcannulas;

FIGS. 38 a and 38 b are schematic plan and rear elevation views,respectively, of a vertebra with an angled catheter partially insertedthrough the second cannula; and

FIGS. 39 a and 39 b are schematic views similar to FIGS. 38 a and 38 b,respectively, showing the angled catheter fully inserted in the vertebrathrough the second cannula.

DETAILED DESCRIPTION OF THE INVENTION

The methods of determining pedicle screw size and placement inaccordance with the present invention is set forth in more detailhereinafter.

Step 1

A computed tomography scan (CT), magnetic resonance image (MRI), CTcapable fluoroscopy or similar two-dimensional imaging study of thespine area of interest may first be obtained. Thin cut sections arepreferable to increase accuracy and detail.

Step 2

A dimensionally true three dimensional computer image of the bony spineis made from the CT, MRI or other studies or in any other suitablemanner, as shown in FIGS. 1 a and 1 b.

Step 3

The three dimensional individual vertebra as shown in FIG. 2 are thenhollowed out by a computer, similar to an eggshell transpedicularvertebral corpectomy, to the specifications desired by the surgeon(i.e., thickness of cortical wall remaining in the vertebral bodycortices or pedicle walls). These specifications allow for asymmetricthicknesses, such that, for example, anterior vertebral body cortexcould be five millimeters thick, lateral vertebral body wall sevenmillimeters thick and the pedicle walls only one millimeter thick; orbody cortical wall uniformly five millimeters thick and pedicle wallsonly one millimeter thick or the like. The individual vertebra can bevisualized as a structure which has been cored or hollowed out and theresulting remaining vertebral body is “electrified” or highlighted in asuitable manner throughout its walls.

Step 4

A computer then automatically determines the maximum allowable diameterscrew to be placed by determining the narrowest diameter or crosssectional area (isthmus) X within any given pedicle based on surgeonpedicle cortical wall diameter preferences, as shown in FIG. 3.

Step 5

A computer then generates an elongated cylinder by starting at thecenter of the isthmus X as a straight line 10 in FIG. 4 which determinesthe ideal axis/trajectory and extending in opposite directions, e.g.,perpendicular to the plane of the isthmus of the pedicle so that it ispositioned concentrically as much as possible within the pedicle withouttouching the remaining cortex with the center of the isthmus being thefulcrum. This line is allowed to penetrate the dorsal or posteriorpedicle cortex so that it can extend beyond the skin of a patient to anydesired length. The line terminates inside the vertebral body to withina predetermined distance (e.g. 5 mm) from the predefined anterior innercortical wall, as selected by the surgeon, so that it does not penetratethe anterior outer cortex and also maximizes screw diameter describedhereinafter.

Step 6

A computer then builds the line 10 concentrically in radial directionsas shown schematically in FIG. 5 to its final maximum diameter whichwill not exceed the narrowest defined pedicle diameter based on surgeonpreference pedicle cortical wall thickness. This concentric buildingultimately grows into a visible cylinder 12 which stops building whenany point on its outer surface comes into “contact” with the highlightedinner cortical wall. The cylinder formed has at its center the beginningline 10 which may be identified in a different color or pattern than theconcentrically built cylinder 12. As described hereinafter, the cylinder12 may be extended beyond its intersection with the dorsal/posteriorcortex to facilitate the placement of screws in accordance with one ofthe automated methods described hereinafter.

Step 7

The maximal diameter allowed may actually be less than that determinedby the narrowest diameter method for those pedicles which have irregularanatomy, as shown in FIG. 6 b, such as curved pedicles (FIG. 7 b) or asimilar deformity. This prevents cortical pedicle wall breach.

Step 8

A computer then determines the length of the screw by measuring thelength of the cylinder 12 starting at the point D in FIG. 8 adjacent tothe predefined anterior inner cortex up to its intersection A with thedorsal/posterior cortex.

Step 9

A computer then provides a data summary table as shown in FIG. 10 awhich displays the ideal pedicle screw diameter, length and trajectory(measured as an angle shown in FIGS. 10 b and 10 c with respect to thetransverse and sagittal planes with corresponding superior end plate asthe reference plane) for each individual vertebra pedicle, and alsoprovides idealized schematic drawings as shown in FIG. 11. Individualvertebra are labeled by having the surgeon identify any specificvertebra as shown in FIG. 9 and then the computer automatically labelsthe remaining vertebral bodies with the surgeon confirming accuratevertebral body labeling.

Step 10

This tabulated data can then be utilized at this juncture fordetermination of the viability of using pedicle screws based on maximalpedicle screw diameter and length, as shown in FIG. 12, and also forplacement of screws by a surgeon's preferred method. FIG. 12 alsoprovides the individual pedicle base circumference outlines (coronaltrajectory) from points A to B and their respective lengths. Actualscrew sizes utilized will be based on surgeon selection of commerciallyavailable screws. A computer can automatically determine and generatethis table once the surgeon provides the available screw size ranges inthe selected pedicle screw system and concomitantly generate anidealized schematic AP (coronal), lateral and transaxial drawing withthe data as shown in FIG. 13. Furthermore, this system provides surgeonoverride capabilities to choose a diameter different than the maximumavailable one on an individual vertebra basis and incorporates theseoverride modifications into the summary data and diagrams.

Step 11—Manual Pedicle Screw Placement

The surgeon may then use the idealized schematic diagram and summarydata for pedicle screw placement based on his or her preferred method.

Step 12a—Pedicle Base Circumference Outline Method—Manual Determination

This method takes advantage of radiographic vertebral body anatomicalandmarks to match the ideal pedicle screw trajectory in the coronalplane as shown in FIGS. 10 d and 11. Specifically, the radiodensitycircular lines seen on standard anteroposterior x-ray or fluoroscopicimages correspond to the pedicle base circumferences. The pedicle basecircumference B is defined as the cortical junction between the pediclewall and its transition into the vertebral body. This pedical basecircumference is distinctly different from the pedicle isthmus, but canin some instances be one and the same or super imposable for individualvertebra as seen in FIGS. 14 a-4 e.

For manual utilization of the pedicle base circumference technique,first the ideal trajectory through the pedicle isthmus X is manuallydetermined using the corresponding transverse radiographic image throughthe pedicle as seen in FIG. 14 b. The pedicle isthmus X is then measuredto determine the maximum diameter pedicle screw. The trajectory isutilized for determination of the maximum pedicle screw length. Thepedicle base circumference B is then determined by identifying thetransition of the pedicle wall into the vertebral body as seen in FIG.14 b. Finally, the length A-B which corresponds to the starting point onthe posterior cortex A up to the intersection with the pedicle basecircumference B is measured and utilized for the calibration of asuitable tool such as variable length awl to be described hereinafter.Point A and point B should be centered with respect to the pedicle basecircumference from the top (cephalad) and bottom (caudad) edges of thepedicle base circumference, as shown in FIG. 14 h. The ideal trajectoryand pedicle base circumference are then combined to determine where thepoint A lies with respect to the anteroposterior projection of thepedicle base circumference and where the point B lies within the pediclebase circumference. This pedicle base circumference outline will have acircular configuration to resemble the anteroposterior radiographicimage for each individual vertebra.

For manual placement of pedicle screws, a standard fluoroscopy unit canbe used to align the superior endplate of the respective vertebral bodyparallel to the fluoroscopic imaging. Furthermore, the vertebral body iscentered when its superior end plate is fluoroscopically visualized bysymmetric disc space with the cephalad vertebral body, and when thevertebral body is equidistant from each pedicle by having the pediclebase circumference outlines visually identical on the fluoroscopic APimage. This centering can still occur when there are other than twopedicles per vertebral body, such as congenital anomalies, tumors,fractures, etc. An appropriately calibrated variable length awl or othersuitable tool T is then placed onto the posterior cortex of thecorresponding vertebral body at pedicle pilot starting hold point Aunder fluoroscopic imaging and advanced into the pedicle up to point Bas seen in FIGS. 14 f and 14 g. This placement is confirmedfluoroscopically and represents two points A and B on a straight linethat co-aligns with the ideal trajectory. The tool T can be readjustedto lengthen and further advance into the vertebral body to point D orexchanged for another pedicle probing awl or similar tool The pedicle isthen sounded for intraosseous integrity, the hold tapped and theappropriate diameter and length pedicle screw is placed transpedicularlyinto the vertebral body.

In accordance with Step 12a, CT transaxial views through center ofpedicles T1, T2, T4, T5, as shown in FIG. 16, demonstrate pediclemorphology, isthmus and manual determination of pedicle pilot hold entrypoints correlating with intraoperative AP fluoroscopic images of eachrespective vertebra. Pedicle screw length, diameter and trajectory havealready been determined. The pedicle base circumference outline isrepresented as the circle on the bottom right hand corner and isutilized as a consistent intraoperative marker for identifying pediclepilot hold starting points. For example, the starting points A for bothT1 and T2 pedicles are approximately 2 pedicle base circumferences and1.25 pedicle base circumferences, respectively, as seen on the APfluoroscopic pedicle base circumference seen intraoperatively (indicatedby the dot within the circle), The T4 and T5 pedicle pilot holes are 0.9and 0.8 pedicle base circumferences, respectively.

Step 12b—Pedicle Base Circumference Outline Method—Semi-Automated

This method is similar to Step 12a except that points A and B andpedicle base circumference outline is determined by a computer afterbuilding the computer generated pedicle cylinders concentrically. Thisdata is then summarized as in FIG. 12. This data also includes thesagittal and transverse trajectory angles measured in degrees withrespect to the superior endplate and midline vertebral body. A variablelength awl or other tool, for example. may then be appropriatelyadjusted to specific pedicle length A-B summarized in FIG. 12 and screwsplaced with standard fluoroscopy as described in Step 12a.

Step 12c—Pedicle Base Circumference Outline Method—Fully Automated

This method further expands the present technique to allow for real-timeimaging and multiple vertebral body visualization for pedicle screwplacement. The data generated is the same as in FIG. 12 except that thepedicle base circumference outlines and identified points A and B aredynamic and do not require the vertebral body to be centered or have thesuperior end plate parallel to the fluoroscopic imaging as in Steps 12 aand 12 b. The fluoroscopically imaged vertebral bodies are registered byany suitable method to the computer generated vertebral bodies withtheir corresponding computer generated pedicle cylinders. The points Aand B are then visualized as seen in FIGS. 15 a . . 15 c and 15 e anddisplayed as in FIG. 12 as updated real-time imaging. A variable lengthawl or other tool. for example. may then be adjusted to appropriatelength for starting at point A and advancing to point B for eachrespective vertebra. It is noted that any suitable tool, such as anonadjustable awl, may be used other than an adjustable awl inaccordance with the methods of the present invention.

Step 13—Adjustable Variable Length Awl

The distance from point A to point B (FIG. 14 b), posterior cortex tointersection with pedicle base circumference, is utilized to set thelength A-B on an adjustable variable length awl constructed inaccordance with the present invention. This awl is used to establish thepedicle pilot hole under fluoroscopic imaging. The pedicle pilot holeforms the first step in a series of steps for actual placement of apedicle screw. The pilot pedicle hole is started at the identifiedstarting point A indicated by the computer generated pedicle cylindersand advanced to point B once it is fully seated.

Referring to FIG. 17 a, the awl 100 comprises a cannulated radiolucenthousing 102 with an open end which movably supports a radio opaque awlmember 104. The awl 100 is fully adjustable for variable lengths tocorrespond to length A-B and also configured to prevent advancement ofthe awl further than any distance A-B as seen in FIG. 14 b and otherdrawing figures.

A surgeon can adjust the awl to any length from point A to point D, thefinal screw length, in FIG. 14 b once the distance A-B has beenradiographically confirmed. The awl 100 preferably is of suchconstruction to tolerate being struck with a mallet or the like and isof a diameter narrow enough to be used percutaneously. To facilitatevisualization of depth, the awl member 104 may be marked in color orotherwise at fixed increments 106, such as 5 mm or 10 mm.

The awl 100 may be provided with a solid head 108 at its outer end forstriking, and with any suitable locking mechanism 110, such as a lockingscrew mechanism, for locking the awl member 104 in a desired positionrelative to the housing 102. The awl may also be provided with a window112 or other indicia for indicating the position or length of the awlmember 104. FIGS. 14 f and 14 g show an awl being advanced into thepedicle to create the screw pilot hole.

FIG. 17 b illustrates a modified adjustable awl 300 which comprises acannulated or hollow awl member 304 and a head 308 with a centralaperture 309 such that a guide wire 311 may extend through the head andthrough the awl member 304 to its inner end. After the pilot hole isformed by the awl 300. the guide wire 31.1 max′ be left in position inthe pilot hole to facilitate its location during subsequent stepsleading to the installation of the pedicle screw.

Step 14—Dual Ring Co-Aligned Technique

For automated intraoperative pedicle screw placement the dimensionallytrue three dimensional spine model with computer automated placedpedicle screw cylinders defining length, diameter and trajectory isutilized. In addition, the pedicle base circumference outline data isutilized to facilitate registration with intraoperative imaging.

Real-time intraoperative fluoroscopy is utilized for accurateregistration with the three dimensional model on an individual vertebralbasis. This fluoroscopic vertebral body image is centered on the monitorand identified by the surgeon for its specific vertebral body identifier(i.e., T2, T3, etc.). The corresponding dimensionally true threedimensional individual vertebral model is registered to thisfluoroscopic image as shown schematically in FIGS. 18 a, 18 b and 18 c.This can be performed on either surgically exposed spines orpercutaneously.

The registration occurs by utilizing internal vertebral body bonylandmarks. These landmarks are the pedicle base circumferences seen onthe fluoroscopic image which arise from the confluence of the pediclecortical walls joining the vertebral body. As hereinbefore explained,these pedicle base circumferences form either circular or ellipticalshapes which can change configuration and square area based on vertebralbody rotation with respect to fluoroscopic imaging.

The intraoperative fluoroscopic and computer spine generated pediclebase circumference outlines are then registered. Precision ofregistration is obtained by assuring outlines are superimposed andmeasured square areas are equal and by assuring distance betweenpedicles is equal. This method of registration eliminates therequirement of having a radiographic marker anchored to the patient'sskeleton, which is particularly disadvantageous, for percutaneousapplications. This method also allows for free independent movement ofone vertebral body to another demonstrating compliance of this computergenerated model, which is particularly useful in spines withinstability. The surgeon confirms adequacy of registration of pediclebase circumferences intraoperatively in order to proceed with screwplacement. This method allows for magnification or reduction of thecomputer generated model to match the intraoperative fluoroscopic image.

The full three dimensional image which now includes the computergenerated pedicle base circumference and pedicle cylinder is thenprojected superimposed on the intraoperative fluoroscopic image. Asshown in FIGS. 19 a and 19 b. the computer pedicle screw cylinder 200 isthen projected out of the patient's body through the posterior cortexand is intercepted by and extends through two separate and collinearrings 202, 204. The rings are mounted on a suitable support frame 206anchored to the patient's bed or other support (not shown) and are sizedto allow interception of the computer cylinder image and to allowplacement of drilling cannulas. The first ring 202 intercepts thecomputer pedicle screw cylinder near the posterior cortical region 208or just outside the body and the second ring 204 intercepts the computerpedicle screw cylinder at any desired distance from the first ring 202.The longer the distance between the two rings the greater the accuracyof screw placement. The interception of the computer pedicle cylinder bythe rings 202, 204 is displayed on a computer monitor which demonstratesmovement of the rings with respect to the computer pedicle cylinder 200.

FIGS. 19 c and 19 d illustrate the computer generated cylinder 200 andline 210 projecting out from a vertebral body VB through the rings 202,204 in a surgically open environment and a percutaneous environment,respectively.

Interception of the pedicle cylinders occurs on two levels. The computerpedicle cylinders 200 are comprised of a central line 210 withsurrounding cylinder. First, the rings 202, 204 need to be centered toboth the central line 210 and pedicle cylinder 200. Second, the ringsare registered to the vertebral body so their movements can be followedon the computer monitor such as through LED devices. Third, the ringsare constructed to have inner diameters to allow matching of diameterscorresponding to the diameter of the computer generated pediclecylinders 200. A variety of removable rings with different diameters maybe provided to allow utilization of any pedicle screw system desired bythe surgeon. Fourth, the rings can be constructed to be adjustable inany suitable manner to allow for variable diameters to allow matching ofdiameters corresponding to the diameter of the computer generatedpedicle cylinder as shown in FIG. 20 where the ring 202 is formed ofmovably connected sections 212 that can be rotated to vary the ringdiameter. Registration of the rings with the computer pedicle cylinderis identified and confirmed on the computer monitor.

The two co-aligned ring 202, 204 now form the conduit in which to placea drilling cannula 214 (FIGS. 21 a and 21 b) which is also secured tothe frame 206 anchored to the patient's bed or other support. Insidethis drilling cannula 214 is placed a solid cannula member 216 (FIGS. 21a and 21 b), or a specialized inner cannula member 218 (FIGS. 2 a and 22b) may be used which has multiple narrow movable and longitudinal metalparallel pins 220 therein and is open centrally to allow for drillplacement. The multiple pins 20 allow for the inner cannula member 218to rest evenly on an uneven surface. This feature provides additionalstability at the posterior cortex drilling area to avoid toggling of thedrill bit.

Additionally, the specialized inner cannula member 218 allows forretraction of the multiple parallel pins to allow fluoroscopicvisualization of drilling within the pedicle. Either method may be usedby the surgeon.

The pedicle is then drilled to its desired precalibrated depth and notexceeding the predetermined pedicle screw length. The pedicle is thensounded with a pedicle probe to assure osseous integrity.

For actual screw placement. a specialized slotted outer cannula 230(FIGS. 23 a and 23 b) is placed collinear and onto the co-aligned tworings 202, 204 which are removably mounted on the support frame. Thisspecialized cannula 230 is also secured to the support frame or otheranchoring device. The rings are then removed by rotating themapproximately ninety degrees (not shown) and withdrawing them from thecannula 230. The slotted cannula's adjustable inner diameter issufficient to accommodate any pedicle screw diameter threaded andvariable head size. The appropriate pedicle screw (not shown) is placedinto its holding screwdriver, placed into the slotted cannula and thenplaced into its respective pedicle.

For the modified adjustable coaligned rings shown in FIG. 20, theslotted cannula 230 in FIG. 23 a can be used or alternatively, the rings202, 204 may be left in position and adjusted to a fully open positionto accommodate a screwdriver placed into and through the rings.

Step 15

There are currently commercially available software packages capable ofproducing intraoperative registration of intraoperative fluoroscopyimages with preoperative three dimensional images of a patient's spine.Such capabilities can be integrated with the methods of the presentinvention to provide summary numerical data and idealized illustrateddiagrams. The latter information will provide the basis for actual screwplacement as described herein or by a surgeon's preferred choice.

Step 16

For surgeons who prefer to place screws extraosseous or extrapedicularbecause the pedicle screw sizes are too small to accommodate availablescrew sizes, planned eccentric screw placement in large pedicles orplanned straight ahead versus anatomic axis screw placement. the presentinvention allows this canability. It accomplishes this by obtaining allidealized data and then allows a surgeon to offset the pedicle pilothole entry placement at any desired distance tangentially from the idealtrajectory. i.e. the anterior screw position is the pivot point D fromwhich a computer pedicle cylinder 12 is generated, as shown in FIG. 24.

Furthermore, these changes will be automatically recorded to generatenew idealized AP, lateral and transaxial schematic diagramsincorporating these changes. This data can be used for placement ofscrews by either the pedicle base circumference method, an automatedaligning method or a commercially available CT/fluoroscopy registrationmethod. For the pedicle base circumference method, new pilot holelengths are determined to allow for proper length of an awl or othertool.

As an illustrative embodiment, FIG. 25 shows schematically theinstallation of a pedicle screw 20 by a screwdriver 22 or the likethrough the center of the isthmus X in accordance with the presentinvention.

Step 17

The new procedure is an extension of the methods described herein forpedicle cylinder building using the pedicle isthmus as the fulcrum forstraight line development. The major difference is that this newprocedure modifies the approach described herein by purposely proceedingwith planned eccentric placement for those vertebras which havepathologic or traumatic features and associated vertebral body abnormalanatomy. For normal vertebral body without endplate fractures orcompression the herein described concentric trajectory through thepedicle is chosen for pedicle cylinder building as seen in FIGS. 26 a,26 b and 26 c.

Step 18

For eccentric pedicle cylinder building the fulcrum for straight linedevelopment remains the narrowest portion of the vertebral body, thepedicle isthmus X. However, once the isthmus is determined, the nextstep is determination of Point D within the vertebral body. This point Dis equidistant from the superior and inferior endplates and in thecenter of the vertebral body abutting the anterior inner cortical wall.A computer then draws a line from Point D to the center of the pedicleisthmus exiting out the posterior pedicle cortex. FIGS. 27 a-c and 28a-c demonstrate trajectory determination for vertebral bodies which havesustained superior endplate and inferior endplate compression fractures,respectively. The FIGS. 25 a-c, 27 a-c and 28 a-c show the planes in thesagittal and transverse where starting points A and B can reside. Thecoronal image demonstrates the effect of combining both the sagittal andtransverse planes to correctly identify the starting points A and B asseen in FIG. 12.

Step 19

A computer then builds this cylinder concentrically in a radialdirection until it comes into contact with the highlighted cortex. Acomputer then determines the ideal pedicle trajectory, diameter andlength and records this into a table (FIG. 12). The pedicle basecircumferences identify the Points A and B for accurate placement of thecombined radioopaque/radiolucent and color banded awl/guide wire intothe pedicle. It is advanced to the appropriate depth distance A-Brecorded in FIG. 12.

Step 20

A banded radioopaque/radiolucent and color banded awl/guide wire, suchas 300/311 in FIG. 17 b, is placed at point A as seen in FIG. 29 andadvanced to point B as seen in FIG. 30. This demonstrates amount ofpenetration by measuring unit lengths seen in fluoroscopic imaging. Oncethe points A and B have been correctly identified then the bandedawl/guide wire 300/311 is advanced to point D (FIG. 31).

Step 21

A first cannulated, banded radioopaque/radiolucent and color bandeddrill bit 400 is then advanced over the guide wire 311 and drilled todepth point D. This is visualized under fluoroscopic imaging as seen inFIG. 32.

Step 22

In one embodiment, a first cannula 500 is then placed over the guidewire 311 and advanced into the pedicle flush with the posterior cortex.The cannula 500 has a radiolucent center 502, a radioopaque collar 504which abuts against the posterior cortex and a radioopaque inner ring506 corresponding to point B based on appropriate length measurements.It is tapped down securely to the posterior pedicle cortex surface asseen in FIG. 33. The guide wire 311 is then removed and a suitableinstrument such as a catheter, cannula or needle is inserted through thefirst cannula into the interior of the pedicle for a desired procedure.

Step 23

In a second embodiment, a second hybrid cannula 600 (FIGS. 34, 35) isadvanced into the first pedicle cannula 500. The second cannula 600 iscomprised of a matching length radiolucent core inner section orcylinder 602 with radioopaque rings 604 on the ends thereof tocorrespond to the pedicle cannula 500. The second cannula also has anouter slotted cannula section 606 that extends beyond the skin forpercutaneous applications. Furthermore, the second cannula has asuitable interlocking mechanism (not shown) with the first cannula 500to facilitate appropriate placement with and removal of the firstcannula as seen in FIG. 35. The interlocking mechanism may be asnap-fit, screw-fit or similar mechanism.

The banded guide wire 311 is then removed and the interlocked firstcannula 500 and second specialized slotted cannula 600 function as aunit, working portal, for kyphoplasty, vertebroplasty or vertebral bodybiopsy instruments, as seen in FIG. 35. For pedicle screw placement asurgeon has a choice for placing screws in the manner described herein.

Step 24

In a third embodiment, the first cannula 500 may be omitted and thesecond cannula 600 may be inserted over the guide wire 311 directlywithin the opening created by the drill bit 400. The guide wire 311 isthen removed and an appropriate instrument is inserted through thesecond cannula 600 into the pedicle for a desired procedure, in themanner shown in FIGS. 36-39.

Step 25

Access for the desired transpedicular procedure then proceeds along thetraditional methods. An improvement of current equipment is a modifiedradioopaque/radiolucent and color banded kyphoplasty balloon catheter,vertebroplasty cannula or vertebral body biopsy needles 700 as seen inFIG. 36 for fluoroscopic imaging.

Step 26

For kyphoplasty procedures a balloon catheter 702 can be introducedstraight and not bent into the first cannula 500 or into the slottedcannula 600, as seen in FIG. 37. The catheter 702 is advanced to theappropriate depth and inflated to proper pressure. Cement or otherinjected suitable material is then placed into the cavitary void createdby the balloon catheter.

Step 27

An improvement over the current balloon catheter or similar instrumentis not only the banding but also the provision of a fixed angled ballooncatheter or instrument 704 as seen in FIGS. 38 a-b and 39 a-b. Theslotted cannula 600 allows the introduction and advancement of theangled balloon catheter 704, which can come in prebent lengths or bemanually bent to a desired angle based on the pedicle length A-B. Oncethe catheter 704 is fully abutted against the posterior pedicle cortex,it is further advanced into the vertebral body by simultaneouslylevering against the lateral aspect of the cannula 600 and forwardpressure. This is visualized on fluoroscopic imaging as seen in FIGS. 39a and 39 b. This new and improved method allows for more centralizedplacement of the catheter 704 within the vertebral body. When fullyinserted in the vertebral body, the outer portion of the catheter 704 isreceived within the slotted cannula section 606. This has substantialadvantages over a bilateral transpedicular approach, such as reducedoperative time, decreased fluoroscopic imaging, the ability to combinewith pedicle screw instrumentation for burst fractures, utilization invertebral bodies with only one radio logically visible pedicle, and usein small volume vertebral bodies.

While many of the steps of the methods of the present invention aredescribed as being computer-generated, it is noted that any suitableapparatus or device may be utilized to accomplish these steps inaccordance with the methods of the present invention.

The invention has been described in connection with what is presentlyconsidered to be the most practical and preferred embodiments. It is tobe understood that the invention is not to be limited to the disclosedembodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of determining the size and/or placement of screws or otherinstruments in pedicles during surgery in a selected spinal area,comprising: using a computer to generate a dimensionally truethree-dimensional image of the bony spine in the selected spinal area;using a computer to hollow out the vertebra in the three-dimensionalimage with cortical wall thicknesses selected by a surgeon performingthe surgery such that the individual vertebra can be visualized as astructure that has been hollowed out with the remaining vertebral bodybeing highlighted throughout its walls; using a computer to determinethe narrowest diameter or isthmus within each pedicle based on thesurgeon's selected pedicle cortical wall thickness; using a computer togenerate a straight line starting at the center of the isthmus andextending inwardly to a point centered within the anterior cortex thatis equidistant from superior and inferior endplates so that it ispositioned concentrically within the pedicle without touching thehighlighted walls thereof, the line terminating inside the vertebralbody a predetermined distance from the anterior inner cortical wall andextending outwardly in the opposite direction to penetrate the posteriorpedicle cortex; using a computer to expand the line concentrically to adiameter that does not exceed the isthmus diameter based on thesurgeon's selected pedicle cortical wall thickness. the line beingexpanded into a cylinder that stops growing when any portion thereofcontacts the highlighted inner cortical wall of the vertebral body withthe exception of the posterior pedicle cortex. using a computer todetermine the length of the cylinder from its innermost end spaced fromthe anterior inner cortical wall to a point at which the outer endthereof contacts the posterior pedicle cortex, and using a computer tocalculate an ideal pedicle screw or instrument diameter, length and/ortrajectory based on dimensions and a trajectory of the cylindergenerated for each pedicle.
 2. The method of claim 1 whereintwo-dimensional images of the selected spinal area are first generated,and then the computer is used to generate the three-dimensional image.3. The method of claim 2 wherein the two-dimensional images are createdby computed tomography scanning (CT), magnetic resonance imaging (MRI),fluoroscopy or similar imaging studies.
 4. The method of claim 2 whereinthe two-dimensional images are thin cut sections for greater accuracyand detail.
 5. The method of claim 1 wherein the center of the isthmusis the fulcrum point for the generated line.
 6. The method of claim 1wherein a computer generates a data summary table which displays theideal pedicle screw or instrument length, diameter and/or trajectory foreach vertebra.
 7. The method of claim 6 wherein the trajectory ismeasured as an angle with respect to the transverse and sagittal planeswith corresponding superior end plate as a reference plane for eachvertebra pedicle.
 8. The method of claim 6 wherein a computer generatesa schematic drawing displaying the idealized pedicle screw or instrumentlength, diameter and/or trajectory for each vertebra.
 9. The method ofclaim 6 wherein a computer is used to determine screw sizes based onscrews that are available for use.
 10. The method of claim 1 furthercomprising the identification of the pedicle base circumference at thejunction between the pedicle base with its vertebral body to enable afluoroscopic AP image scan intraoperatively to correlate with apreoperative three-dimensional image generated by the computer fordetermining pedicle screw or instrument placement and measurements basedon an outline of the pedicle base circumference.
 11. The method of claim10 further comprising a projection of the outline of the pedicle basecircumference outwardly to the posterior pedicle cortex in accordancewith the predetermined screw or instrument trajectory to identify astarting point for the screw or instrument on the posterior cortex. 12.The method of claim 10 wherein a circle is created to correspond withthe pedicle base circumference in the intraoperative fluoroscopic imageand a pedicle screw pilot hole is determined by viewing where it lieswith respect to the circle and the posterior cortex.
 13. The method ofclaim 12 wherein real time intraoperative fluoroscopy is used forregistration with the three-dimensional image for each vertebra.
 14. Themethod of claim 12 wherein the pedicle screw or instrument pilot hole isoffset for eccentric screw placement by rotation of an ideal cylindertrajectory tangentially with a pivot axis being the innermost end of thecylinder adjacent to the anterior inner cortical wall.
 15. The method ofclaim 1 wherein a portion of the generated line and cylinder extendingbeyond the posterior pedicle cortex is used to facilitate automatedintraoperative pedicle screw or instrument placement.
 16. A method ofdetermining the size and/or placement of screws or other instruments inpedicles during surgery in a selected spinal area, comprising:generating a dimensionally true three-dimensional image of the bonyspine in the selected spinal area; hollowing out the vertebra in thethree-dimensional image with cortical wall thicknesses selected by asurgeon performing the surgery such that the individual vertebra can bevisualized as a structure that has been hollowed out with the remainingvertebral body being highlighted throughout its walls; determining thenarrowest diameter or isthmus with each pedicle based on a Surgeon'sselected pedicle cortical wall thickness; generating a straight linestarting at the center of the isthmus and extending inwardly to a pointcentered within the anterior cortex that is equidistant from superiorand interior endplates so that it is positioned concentrically withinthe pedicle without touching the highlighted walls thereof, the lineterminating inside the vertebral body a predetermined distance from theanterior inner cortical wall and extending outwardly in the oppositedirection to penetrate the posterior pedicle cortex; expanding the lineconcentrically to a diameter that does not exceed the isthmus diameterbased on the surgeon's selected pedicle cortical wall thickness, theline being expanded into a cylinder that stops growing when any portionthereof contacts the highlighted inner cortical wall of the vertebralbody with the exception of the posterior pedicle cortex; determining thelength of the cylinder from its innermost end spaced from the anteriorinner cortical wall to a point at which the outer end thereof contactsthe posterior pedicle cortex; and calculating an ideal pedicle screw orinstrument diameter, length and/or trajectory based on dimensions and atrajectory of the cylinder generated for each pedicle.